208 MR. F. E. BEDDARD ON THE [Feb. 19, 



c. Azygos only present on right. No I'udiment on left side. 

 Macropus melanotis. 



d. Azygos large on left side, with a rudiment only on right 



side. 

 Trichosmms vidpeciila, Dromicia nana, j-Epyprymnus rufescens, 

 Onychogale frenata. 



e. Azygos on left side only. No rudiment on right side. 

 Dendrolagus bennettii, Didelphys nudicaudata, Pseudochirus, 



Perameles obestola, Petatcrus brevicejjs, Phascologale penicillata, 

 Dasyurns onaiijgcei. 



(8) Rodents. 



Of the azygos in this order of Mammalia Owen wrote that 

 " opposite proportions [to those shown by the azygos veins of the 

 Hedgehog] prevail in Leporidte and some other Rodents, as in 

 Squirrels, the left azygos being small or wanting." This state- 

 ment is largely but not entirely true, as will be seen in the course 

 of the following description of several genera and species of 

 Rodents. In view of the fact that so many Rodents possess, as 

 is well known, both precaval veins, it might be expected that 

 here, as among the Marsupials, where a like condition of the pre- 

 caval exists, there would be traces of both right and left azygos. 

 And this is precisely what is found among the Rodentia. 

 It is for this reason that I treat of the Rodents next to the 

 Marsupials. 



The most remarkable condition of the azygos vein so far as 

 concerns the Rodentia is seen in the Beaver. But as I have only 

 had the opportunity of dissecting a single example of this Rodent, 

 the structure may be abnormal in the individual. There is only 

 a single azygos ; but the vein, instead of lying upon the right 

 side, as is otherwise the case when the vein in question is only 

 developed upon one side of the body, lies upon the left side. 

 This state of aflairs is, however, only an exaggeration of that 

 found in Jactdus orienfalis. In this Rodent, as I have ascertained 

 and shall point out, of the two azygos veins present that of the 

 left side is the larger instead of, as in the majority of cases where 

 there are two azygos and a discrepancy in size between them, the 

 right being the larger. 



This condition of the azygos, however, exists among the Mar- 

 supials, as has already been pointed out*, and also among the 

 Ungulates t, but apparently nowhere except as an anomaly. 



Of Gapromys pilorides I have had the opportunity of studying 

 two examples which, although they present certain diflerences, 

 agree in cei'tain main featiu'es in which they also present unmis- 

 takable points of likeness to their allies Hystrix and Dolichotis. 



The azygos is either only or almost entirely to be found on the 

 right side +. The vein on that side in one specimen follows after 



* Supra, p. 202. t Svpra, p. 190. 



X Dobson (P. Z. S. 1884, p. 248) only mentions a left azygos. 



